Effects of spark plasma sintering parameters on sintering mechanism of yttrium hydride

Yttrium hydride (YH x ) is a highly promising neutron moderator material for nuclear reactors, known for its exceptional thermal stability and high hydrogen content. This study investigated the sintering mechanism and microstructural evolution of YH x monoliths processed by spark plasma sintering (SPS), with the effects of temperature, duration, and pressure. The results indicate that the sintering process can be divided into five stages: formation of sintering necks, rapid densification, anti-densification, recrystallization, and grain growth. The anti-densification behavior is attributed to hydrogen desorption, phase transformation-induced volumetric contraction, and vacancy coalescence from hydrogen migration, leaving residual pores and lattice defects. Furthermore, increasing the sintering temperature and duration promotes recrystallization and grain growth, whereas elevated pressure effectively suppresses grain boundary migration. This research establishes fundamental processing-structure correlations critical for optimizing YH x moderators in nuclear applications.